Power cable



- March 24, 1970 W.G.DIAHLSTROM V 3,502,191

POWER CABLE Filed Dec. 12, 1968 4 r l y y CONDUCTOR V5 N TOR rm 6.OAHLSTROM' I Attorney United States Patent Office 3,502,791 POWER CABLEWalter G. Dahlstrom, Worcester, Mass., assignor to United States SteelCorporation, a corporation of Delaware Filed Dec. 12, 1968, Ser. No.783,265 Int. Cl. H01b 7/04, 9/00 US. Cl. 174115 9 Claims ABSTRACT OF THEDISCLOSURE This invention relates to electrical power cable and, moreparticularly, to improvements in mine trailing cable used to providepower to shuttle cars in mines. Such cables are attached at one end to asource of power in the mine and at the other end to a reel on theshuttle car. As the car moves in the mine, the cable is either paid outor taken up depending upon the direction of travel of the shuttle car.These cables usually have at least two parallel rubber insulatedconductors surrounded by an integral rubber jacket. The conductors areseparated from one another by the jacket or by such devices as a fabricstrip. The cable may include grounding wire. The cable must be flexibleand be able to withstand much mechanical abuse. Movement of theinsulated conductors within the jacket is restricted such as by a cementbonding the insulated conductor to the jacket. This restricts themovement of one insulated conductor with respect to the other so thatone insulated conductor cannot elongate relative to the other, which mayresult in buckling of the jacket and actual penetration through thejacket.

These cables are usually fabricated by extruding insulation material,for example about .0625 inch thick for a size 4 A.W.G., 600 volt ratedcable, over the conductors individually and then extruding the jacketover the insulated conductor and grounding wires.

Insulating properties and mechanical strength of the cable have beenimproved by substituting a thin polyolefin insulation for the relativelythick rubber insulation. This permits increasing the jacket thicknesswhile retaining the same external dimensions, thus providing moremechanical protection to the insulated conductors. However, sinceattempts to bond the insulated conductors to the jacket have beenunsuccessful, these polyolefin insulated cables have a shorter life thanif they were bonded because movement of the insulated conductors hasbuckled and ruptured the jacket. Even if a bond between the insulatedconductors and the jacket could be developed,

it would still be necessary to control the bond to facilitateterminating and splicing the cable.

According to my invention, the conductors are insulated and joined by aconnecting web of insulating material in a single extrusion. The web isthen perforated. The jacket material penetrates the perforations andmechanically locks the separate conductors and jacket in fixed positionwith respect to each other.

It is, therefore, an object of my invention to provide a multipleconductor cable in which the conductors and jacket are mechanicallylocked from movement with respect to one another.

Another object is to provide such a cable in which the conductors resistbuckling and do not penetrate the jacket.

A further object is to provide such a cable wherein the conductors donot move with respect to each other.

3,502,791 Patented Mar. 24, 1970 A still further object is to providesuch a cable in which the insulation is not bonded to the jacket.

These and other objects will be more apparent after referring to thefollowing specification and attached drawing in which:

FIGURE 1 is a cross-sectional view of the improved cable of myinvention; and

FIGURE 2 is a plan view of a fragment of an insulated conductor and webassembly of my invention before the application of the protective jacketand ground wires.

Referring now to the drawing, reference numeral 2 indicates two spacedapart generally parallel stranded conductors surrounded by insulation 4.Conductors 2 may be copper, aluminum, or other suitable conductingmaterial in any suitable form such as the seven-wire strand shown.Insulation 4 is preferably an insulating compound containing polymers ofa polyolefin with a suitable wall thickness for the voltage rating andsize of the cable, for example about 0.020 inch for a 600 volt size 4A.W.G. cable. However, polymers of polyvinyl chloride, chlorosulfonatedpolyethylene, polyisoprene, butadiene-styrene, ethylene-propylene, orpolychloroprene are also satisfactory. The insulated conductors 2 areconnected by a web 6 of the insulating material integral with theinsulation 4. Web 6 has perforations 8 throughout the length of thecable. A protective jacket 10, preferably a compound containing polymersof polychloroprene, surrounds the insulated conductors 2 and the web 6filling the perforations 8, thus locking the jacket to theinsulation-web structure. Jacket 10 may also be other jacketingmaterials commonly used for electrical cables, such as compoundscontaining polymers of polyvinyl chloride, chlorosulfonatedpolyethylene, polyurethane or butadiene acrylonitrile-polyvinylchloride. A pair of grounding wires 12 of suitable capacity and materialare embedded in jacket 10 one on each side of web 6.

Web 6 should be thin enough to maintain the desired flexibility of thecable while being thick enough to keep conductors 2 separated. Web 6 maybe as thin as 5 mils. Perforations 8 are preferably round or elliptical.The surface areas of the perforations 8 with respect to the surface areaof the web 6 should be no more than nor less than 10%.

Web 6 is shown as being located generally in the plane passing throughthe axes of the conductors. While such a location is preferred, otherconfigurations would also be satisfactory, such as a web in a planeparallel to the plane passing through the center line of the conductorsbut tangent to the outer circumferences of the insulation.

Ground wires 12 may be omitted or replaced by a single ground wire or bymore than two ground wires depending on the current-carrying capacityrequired and geometry of the cable.

While the cable is shown with two conductors, other combinations such asa flat cable with three parallel conductors and two connecting webswould have the same desirable characteristics.

In making the cable, a single extrusion is required for the insulationand web. The perforations may be made in a conventional manner as theconductor assembly leaves the extrusion die. The jacket is then extrudedover the conductor assembly and ground wire.

The jacket rubber penetrates the perforations and thus locks the jacketto the conductor assembly. This results in a cable insulation that has atendency to resist twisting and to lie flat, and facilitates theseparation of the jacket and the insulation for splicing and terminalconnections. The preferred construction of the cable is with theinsulating material and web as an integral assembly, but the flexibilityand spacing control could also be effective with the web and insulationof different materials bonded or cemented to each other.

While several embodiments of my invention have been. shown anddescribed, it will be apparent that other adaptations and modificationsmay be made.

I claim:

1. A multiple conductor power cable comprising two generally parallelspaced apart electrical conductors, a layer of electrical insulatingmaterial surrounding each conductor, a perforated web joining the layersof electrical insulating material along longitudinal edges of the web,and a jacket of protective material surrounding said web and theinsulated conductors, said protective material penetrating theperforations to mechanically lock the conductors and jacket in fixedpositions with respect to each other.

2. A cable according to claim 1 in which said jacket material is acompound containing at least one polymer of the group consisting ofpolychloroprene, polyvinyl chloride, chlorosulfonated polyethylene,polyurethane, and butadiene acrylonitrile-polyvinyl-chloride.

3. A cable according to claim 1 in which the area of the webperforations is between approximately 10% and 90% of the web area.

4. A cable according to claim 1 in which the said web is insubstantially the same plane as the axes of said conductors and isintegral with said layers of insulating material.

5. A cable according to claim 4 in which said insulating material is acompound containing at least one polymer of the group consisting ofpolyolefin, polychloroprene, polyvinyl chloride, chlorosulfonatedpolyethylene, polyisoprene, butadiene-styrene, and ethylene-propylene.

6. A cable according to claim 5 in which said jacket material is acompound containing at least one polymer of the group consisting ofpolychloroprene, polyvinyl chloride, chlorosulfonated polyethylene,polyurethane, and butadiene-acrylonitrile-polyvinyl-chloride.

7. A cable according to claim 6 including a pair of grounding conductorswithin the jacket, tone on each side of said web generally parallel tosaid two conductors.

8. A cable according to claim 7 in which the area of the webperforations is between approximately 10% and E. A. GOLDBERG, PrimaryExaminer US. Cl. X.R. 174-113,

